Apppresser has recently announced it's an extension for WooCommerce stores called WooCommerce Smart Checkout. It makes the mobile checkout experience better by offering a multi-step checkout process, autofill address integration, and other mobile optimizations. The changes are all geared to improve mobile conversions, which tend to be significantly lower than desktop.
The product is in private beta and you can sign up on the site. I tested it today, both with the mobile version and desktop version, and I was overall pretty impressed. It definitely improves the default mobile experience, and I like the tabbed step-by-step process. I'm not sure I'm in love with the desktop modal, though that's not the primary use case. For mobile checkout, I think this is a good plugin that serious shop owners may be able to make good use of.